Chrominance subcarrier component-selection system



6 Sheets-Sheet 1 B. D. LOUGHLIN CHROMINANCE SUBCARRIERCOMPONENT-SELECTION SYSTEM Sept. 26, 1961 Original Filed Oct. 5. 1953c-lll CHROMINANCE SUBCARRIER COMPONENT-SELECTION SYSTEM original Filedoct. 5. 1955 Sept. 26, 1961 9;. D. LouGl-ILIN 6 Sheets-Sheet 2 FIG. 3

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FI G 4 a Sept. 26, 1961 B. D. LOUGHLIN CHROMINANCE SUBCARRIERCOMPONENTSELECTION SYSTEM Original Filed 0G12. 5. 1953 6 Sheets-Sheet 5o VIDEO 25 FREQUENCY AMPLIFIER www 6 Q mw @FU N 6 0 A U O 0 D K R O OCRR \1RST MEO O HUG BTW 5 COE LTI NNT N s l o o o 4 2 c a o o R me G Y lAW ml 2W Emw Ll 4 4L STU EL 2 P ASC D 3m wmp o o o o m0 w o 9x 4 TmeFlGln Sept. 26, 1961 B. D. I ouGI-ILIN 3,002,049

CHROMINANCE SUBCARRIER COMPONENT-SELECTION SYSTEM Original Filed Oct. 5.1953 6 Sheets-Sheet 6 O O- IO 0"'3MC DELAY FILTER oNETwoRK o vIDI-:oo 25FREQUENCY o AMPLIFIER o o 0 -J PUSH-'PULL 22 AMPLIFIER "1- FIGA3,002,049 CHROMFNANCE SUBCARRTER COMPONENT- SELECTION SYSTEM v BernardD. Loughlin, Lynbrook, NY., assignor to Hazeltine Research, Inc.,Chicago, Ill., a corporation of illinois @riginal application Uct. 5,1953, Ser. No. 384,237, now Patent No. 2,734,940, dated Feb. 14, 1956.Divided and this application Jan. 20, 1956, Ser. No. 560,412

11 Claims. (Cl. 178-S.4)

General The present invention is directed to chrominance subcarriercomponent-selection systems useful. in imagereproducing systems ofcolor-television receivers and, particularly, useful in a compatiblecolor-television receiver utilizing a picture tube having -a singleelectron gun for reproducing either color or monochrome images.v

This application is a division of application Serial' No. 384,237, filedyOctober 5, 1953, now U.S. Patent No. 2,734,940, issued February 14, 1956, and entitled Image- Reproducing System for A Color-TelevisionReceiver.

ln a form of color-television system more completely described in anarticle in the magazine Electronics for February 1952, entitledPrinciples of NTSC Compatible Color Television at pages 88-95,inclusive, information representative of a scene in color beingtelevised is developed `at the transmitter two substantiallysimultaneous signals, one of which is primarily representative of thebrightness or luminance and the other of which is representative of thechromaticity of the image. The latter signal is a subcarrier Wave signalthe frequency of which is Within the band Width of the brightnesssignal. This subcarrier wave signal has successive cycles each modulatedin phase by signal components representative of primary colors or huesso that the cycles have substantially the same phase-hue characteristic.In such'subcarrier Wave signal the successive cycles lare also modulatedin amplitude by signal components representative of the color saturationof successive elemental areas of the televised color image. yThecomposite video-frequency signal comprising the brightness signal andthe modulated subcarrier wave signal is one developed by the NationalTelevision System Committee (NTSC) for the translation of informationrepresentative of the color ofthe televised image and Will be referredtohereinafter as the NTSC signal. This composite signal is` utilized tomodulate a conventional radio-frequency carrier-Wave signal.

A receiver in such system intercepts the radio-frequency signal andderives the NTSC signal therefrom. One type of such receiver includes apair of principal channels for applying the brightness and chrominanceinformation to an image-reproducing device therein. The channel fortranslating the brightness signal is substantially the same -as thevideo-frequency amplifier portion of a conventional monochrome receiver.The chrominance signal` is translated through the second of suchchannels and three color-signal components individuallyl representativeof the three primary hues or colors red, green, and blue of the imageare derived therefrom and are combined with the brightness signal in theimage-reproducing device to effect reproduction of the televised image.

One form of image-reproducing device of the type just mentionedconventionally includes a cathode-ray tube having three electron guns,the three color-signal4 components being individually applied toldifferent ones of the guns While the brightness signal is applied toeach thereof. The electron beams emitted from the three guns areutilized individually to excite diierent ones of three phosphors whicheffectively develop three primary color images, such images being'optically combined to reproduce the televised image. Such ya device,because of the 3,002,049 Patented Sept. 26, 1,961

ICC

utilization of three separate subsidiary channels in the principalchrominance channel for translating the color information tothedifferent phosphors n the cathode-ray tube, is subject to registrationproblems of the three' primary color images developed by such phosphors.Such problems arise from the lack of proper relative alignment of thethree electron beams when exciting the phosphors to develop thedifferent color images. As a result, there is a tendency in such device,unless adjustments which tend to be exceptionally ne and critical aremade andn maintained, to have undesirable overlapping of images causinglow denition and spurious color effects especially on the edges ofyobjects therein. Additionally, when utilizing such a device and theinherent three beam circuits in the picture tube for translating' boththe monochrome and color information there is a problem of criticallybalancing the relative intensities o-f the three beams so that they willhave proper relative intensities to combine in the cathode-ray tube toreproduce -a blackand-White image over the entire brightness range whenonly monochrome information is being received. Because of theabove-described deficiencies in such multicolor channel devices, it ispreferable to utilize a singlegun picture tube, thereby facilitating theutilization of a single channel for all of the monochrome and colorinformation,l provided other complexities in utilizing such tubes do notoifset the advantages. By utilizing such single colorv channel, if thedifferent colors are selected at the image screen of the picture tube,the above-mentioned registration problems` are solved and the problem ofcritical balancing of the gains of 'diiferent color channels disappears.y

A single-gun tube of a type considered desirable has recently beenydescribed in the Proceedings of the I.R.E. for July 1953 at pages851-858, inclusive, in an article The PDF Chromatron-A Single orMulti-Gun Tri- Color Cathode-Ray Tube. This tube hereinafter referred toas the single-gun tube will be more -fully considered hereinafter.However, there is one problem in utilizing such single-gun tube in thatthe three primary color images are sequentially reproduced by causingthe electron beam therein periodically to impinge upon the diiferentphosphors for developing the different component colors of thereproduced image and, as presently defined-the NTSC signal, for reasonsto be discussed more fully herein-after, does not lend itself to directapplication to Such-tube if high-quality Icolor reproduction is to beobtained. In the NTSC signal, the color components modulating differentphase points of the subcarrier Wave signal are not in proper phaserelation and do not have proper relative intensities to cooperate withthe impinging of the electron beam on the different phosphors'v todevelop the primary color images. If the NTSC signal is directly appliedto such tube, there tend to be col'or distortion and a loss of constantluminance in the reproduced image.

lt has been proposed that such tube be utilized to reproduce acolorimage from the NTSC signalA by initially deriving fromJ such signalbefore applicationA to the picture tube the signals representative ofthe three primaryr colors therefrom tor obtain three simultaneous colorAsignals. These derived color signals are then sequentially sampled atthe correct times to develop a composite signal. The latter signalincludes color components which, when applied to the single-gun tube,cooperate with the electron beamI as it sequentially impinges on thediiferent color phosphors to cause the different color signals tomodulate the intensity of the beam as it impinges on corresponding onesof the color phosphors. Such decoding of the NTSC subcarrier Wave signaland re-encoding by means of a sampling device is undesirable since theaforementioned problem of critically balancing the gains of threechannels to obtain signals for reproducing desirable black-and-whiteimages over the brightness range is introduced thereby. It is preferableto modify the NTSC signal directly, that is, without any decoding of thecolor components thereof so that the modified signal may be directlyapplied to the single-gun tube to reproduce acceptable color andblack-and-white images. This modification can be accomplished by meansincluding chrominance component-selection systems constructed inaccordance with the invention.

It is an object of the present invention, therefore, to provide a newand improved chrominance componentselection system for deriving achrominance component of the NTSC signal directly, that is, without anydecoding.

It is another object of the invention to provide a new and improvedchrominance component-selection system useful in an image-reproducingsystem for a colortelevision receiver including a single-gun type ofpicture tube.

It is another object of the invention to provide a new and improvedsystem capable of selecting a chrominance component along a given axisof a chrominance subcarrier signal to the substantial exclusion of itsquadrature component.

In accordance with a particular form of the invention, in acolor-television receiver, a system for selecting a chrominancesubcarrier component along a predetermined axis of a receivedchrominance subcarrier signal comprises first circuit means forsupplying a chrominance subcarrier signal and second circuit means forsupplying a reference signal having a second harmonic frequency relationto the subcarrier signal. The system also includes third circuit meanscoupled to the first and second circuit means and being, under thecontrol of the reference signal, responsive to the subcarrier signalduring phase angles when a selected subcarrier signal component along apredetermined axis has maximum magnitude for developing a subcarriersignal representative of the selected subcarrier component to thesubstantial exclusion of its quadrature component.

For a better understanding of the present invention, together with otherand further objects thereof, reference is had to the followingdescription taken in connection with the accompanying drawings, and itsscope will be pointed out in the appended claims.

Referring to the drawings:

FIG. 1 is a schematic diagram of a color-television receiver includingan image-reproducing system in accordance with the invention describedand claimed in applicants above-mentioned copending parent application;

FIG. 1a is a diagrammatic representation of the image screen of thepicture tube utilized in the receiver of FIG. 1;

FIG. 1b is a circuit diagram of the image-reproducing system of FIG. 1;

FIGS. lc-lh, inclusive, 1k, 1m, and 1n are explanatory diagrams utilizedin explaining the operation of the system of FIG. 1b;

FIG. 2 is a circuit diagram, partially schematic, of a modified form ofthe image-reproducing system of FIG. 1 including a chrominancesubcarrier component-selection system constructed in accordance with theinvention;

FIG. 3 is a circuit diagram, partially schematic, of another form of theimage-reproducing system including a chrominance subcarriercomponent-selection system constructed in accordance with the invention;

FIG. 4 is a schematic diagram of another modified form of theimage-reproducing system including a chrominance subcarriercomponent-selection system constructed in accordance with the invention,and

FIG. 4a is a vector diagram utilized in explaining th operation of thesystem of FIG 4.

General description of receiver of FIG. 1

Referring now to FIG. 1 of the drawings, there is represented acolor-television receiver of the superheterodyne type such as may beused in a color-television system of the type previously discussedherein and in the aforesaid Electronics article. The receiver includes acarrier-frequency translator 10 having an input circuit coupled to anantenna system 11. It should be understood that the unit 10 may includein a conventional manner one or more stages of wave-signalamplification, an oscillator-modulator, and one or more stages ofintermediate-frequency amplification if such are desired. Coupled incascade with the output circuit of the unit 10, in the order named, area detector and automatic-gain-control (AGC) supply 12, and animage-reproducing system 13 constructed in accordance with the presentinvention and to be described more fully hereinafter.

An output circuit of the detector 12 is coupled through asynchronizing-signal separator 14 to a line-scanning generator 15 and afield-scanning generator 16, output circuits of the latter units beingcoupled, respectively, through the pairs of terminals 17, 17 and 18, 18to linedeection and field-deflection windings of the image-reproducingapparatus in the image-reproducing system 13. Additionally, an outputcircuit of the separator 14 and of the generator 15 are coupled througha gated color burst signal amplier 19 and -a phase-control system 20, incascade, to a color reference-signal generator 21 for developing a 3.6megacycle sine-wave signal. The output circuit of the generator 21 iscoupled through a pair of terminals 22, 22 to a push-pull amplifier 35in the image-reproducing system 13, and an input circuit of thephase-control system 20 is coupled through another pair of terminals 23,23 to the aforementioned push-pull amplier. 'I'he amplifier 19 may be ofa conventional gated type for periodically translating a color burstsynchronizing signal during its occurrence, and the phase-control system20 may be a conventional automatic-phase-control system for utilizing acolor burst synchronizing signal to control the frequency and phase ofthe signal developed by the generator 21.

The AGC supplyof the unit 12 is connected through the conductoridentified as AGC to input terminals of one or more of the stages in theunit 10 to control the gains of such stages to maintain the signal inputto the detector 12 within a relatively narrow range for a wide range ofreceived signal intensities. A sound-signal rcproducing system 24 isalso connected to an output circuit of the unit 10 and it may includestages of intermediatefrequency amplification, a sound-signal detector,stages of audio-frequency amplification, and a sound-reproducing device.

It will be understood that the various units and circuit elements thusfar described with the exception of the image-reproducing system 13 maybe of conventional construction and design, the details of such unitsbeing well known in the art and require no further description.

General operation of receiver of FIG. 1

detector 12 to develop a composite video-frequency signal of the NTSCtype. The latter signal comprises synchronizing components, theaforementioned subcarrier wave signal or chromaticity signal, and theaforementioned luminance or brightness signal. The derivedvideo-frequency signal is applied through a pair of terminals 25, 25 tothe image-reproducing system 13.

The synchronizing components including line-frequency andfield-frequency synchronizing signals as well as the aforementionedcolor burst signal for synchronizing the operation of the generator 21are separated from the rother video-frequency components and at -leastsome of such synchronizing signals are separated from each other in thesynchronizing-signal separator 14. The line-frequency andfield-frequency synchronizing components are applied, respectively, ltothe units 15 and -1-6 to synchronize the operation thereof with theoperation of related units at the transmitter. These generators supplysignals of saw-tooth wave form which are properly synchronized withrespect to the transmitted signal and are applied to the line-dellectionand held-deflection windings of the color image-reproducing apparatus inthe system 13 to eifect a rectilinear scanning of the image screen ofthe picture tube in such system. The color burst signal, which issubstantially a few cycles of an unmodulated portion of theaforementioned subcarrier wave signal and has a desired reference phasewith respect to such subcarrier wave signal, is translated through theamplitier 19, when suchV amplifier is gated on by a line-retrace signalfrom the generator 15 during the line-blanking period and is applied tothe phase-control system 20 to control the frequency and phase of thesignal developed in the generator 21.

In the image-reproducing system 13, as will 4be described more fullyhereinafter, the information representative of the different primarycolor images is derived from the composite video-frequency signalappliedthereto from the output circuit of the detector 12 and is utilized tomodulate the intensity of the electron beam in the picture tube in thesystem 13. This intensity modulation together with other controlling ofthe beam in the picture tube results in the excitation of the differentcolor phosphors therein iii coincidence with the occurrence ofinformation representative of the corresponding one of the differentprimary colors to reproduce three primary color images. These primarycolor images are optically combined to reproduce the complete colorimage. Y Y

The automatic-gain-control or AGC signal developed in the unit 12 iseffective to control the amplification of one or more of the stages inthe unit thereby to maintain the signal input to the detector 12 and tothe sound-signal reproducing system 24 within a realtively narrow rangefor a wide range of received signal intensities. The sound-signalmodulated wave signal, having been selected and amplified in the unit10, is applied to the sound-signal reproducing system 24. Therein it isamplified and detected to derive the sound-signal modulation componentswhich may be further amplified and then reproduced in the reproducingdevice of the system 24.

Description of image-reproducing system of FIG. 1

In describing the image-reproducing system 13 of FIG. 1, the combinationof the units thereof comprising the complete system will first beconsidered with reference to lFlG. l and then the details of specificembodiments of such units will be considered with reference to FIG 1 b.The image-reproducing system of FIG. l comprises a circuit for supplyingan NTSC signal including a first component primarily representative ofthe brightness and a subcarrier wave signal representative of thechromaticity of a televised image. More specifically, such circuitcomprises a video-frequency amplifier 28 having an input circuit coupledto the pair of terminals 25, 25. The NTSC type of signal is such as haspreviously been described herein and the subcarrier wave signal isonewhich has been modulated at the transmitter at different phase pointsthereof by signals representative of the chromaticity of the image. Morespecifically, such subcarrier wave signal has successive cyclesmodulated at phase points in each cycle by signal componentsrepresentative of hue so that the cycles have substantially the samephase-hue'characteristic. These cycles are yalso modulated .in amphtudeby components representative of the color saturation of' successiveelemental areas of the televised color image.r More complete details ofsuch signal are discussed in the aforementioned Electroncs article. 'Iheimage-reproducing system also comprises a color image-.reproducingapparatus, specifically, apparatus 29 including a cathode-ray tube 30`yhaving a multicolor image screen 31 and means for scanning the screenwith an electron beam, the scanning means including means forconditioning the apparatus 29V to develop a plurality of colors in a`sequence repeating at `a predetermined frequency in which one `of thecomponent colors occurs twice. `More specifically, the means forscanning the screen with an electron beam includes a conventionalelectron gun in the cathode-ray tube, conventional lineandfield-deicction windings 32, and -a grid-like structure 33 parallel toand spaced a short distance from the screen 311 between the yelectrongun and the screen and having the grid wires thereof coupled through atransformer 34 to the output circuit of a push-pull amplier 3S. The.elements 33, 34, and 35comprise means for conditioning the apparatus-29toI develop'a plurality of colorsV in a sequence repeating at apredetermined frequency, in a manner to be explained more fullyhereinafter. More specically, the picture tube 30 is a single-gun typesuch as described in the aforesaid IRE article. The image screen 31 ismore Ifully represented in FIG. la and includes repeating groups ofthree parallel strips of different phosphors individually for emittingthe green, red, and blue colors indicated. The grid structure 33comprises a plurality of conductors which are parallel to each other'and the phosphor strips on the l.screen '31, one of such conductors4being positioned between each of the phosphor strips for emitting redand blue colors and the electron gun of the tube 30, there being no suchconductors similarly positioned with respect to the phosphor strips foremitting green. The conductors adjacent the strips for emitting red areconnected together and to one side of the winding of the transformer 34while those adjacent the phosphor strips -for emitting blue are alsoconnected together and to the other side of suoli winding.

.The image-reproducing system 13 of FlG. l also coinprisessignal-modifying apparatus coupled to the aforesaid supply circuits,speci'ically, to the amplifier 28 for translating the modulatedsubcarrier wave signal at a predetermined phase with respect to theabove-mentioned sequence of colors developed on the image screen of theimage-reproducing apparatus 29 and for deriving from the subcarrier wavesignal a modulated Wave signal differing in frequency therefrom -andwhich is a harmonic of the above-'mentioned predetermined frequency andhas Ia predetermined phase with respect to the aforesaid sequence. Morespecifically, such signal-modifying apparatus eifectively includes afirst signal-translating channel, specifically, a delay line 4t), aO-4.2 megacycle filter network 41, and a direct-current restorer 42connected in cascade in the order named between theoutput circuit of theamplifier 28 and the control electrode of the picture tube 30. The unitseil, w1, and 42 comprise the channel `for translating the aforesaidmodulated subcarrier wave signal at a predetermined phase, to bediscussed more fully hereinafter, with respect to the sequence in whichthe colors are developed on the image screen 31 of the tube 3), andfurther are the channel for translating the brightness or luminancesignal for application to the tube 30.

The signal-modifying apparat-us also includes a secondsignal-translating channel, specifically, la channel including a 3.0-4.2rnegacycle iilter network 43, a modualtor 44, and a 6.6-7.8 megacyclefilter network 45 connected in cascade, in the order named, between theoutput circuit of the amplifier 28 and the cathode of the picture tube30. The second signal-translating channel also includes ya thirdharmonic amplifier 46 coupled between an output circuit of the push-pullamplifier 35 and -an input circuit of the modulator 44 for devewpinsaSignal, the freiusncy '7 of which is approximately 10.8 megacycles orthe third harmonic of the 3.6 megacycle signal developed in the outputcircuit of the amplifier`35.

The signal-modifying apparatus may also include a second harmonicamplifier 47 for developing gating signals which are the sixth harmonicof the 3.6 megacycle signal developed in the output circuit of theamplifier 35, that is, which have a frequency of approximately 21.6megacycles for application to the screen electrode of the picture tube30. The circuit connecting the output circuit of the amplifier 47 to thescreen electrode of the picture tube 30 includes a switch 48 yforselectively making such connection. The signal-modifying apparatus mayalso include -a phase-adjusting circuit 49, a synchronous detector 50,and a -0.6 megacycle filter network 51 connected in cascade, in theorder named, between an output circuit of the push-pull amplifier 35 andan input circuit of the filter network 41 vfor developing luminancecorrection signals for combination with the received luminance signalsto develop -a luminance signal suitable for use in the picture tube 30.An input circuit of the synchronous detector 50 is coupled to an outputcircuit of the filter network 43 for applying the modulated subcarrierwave signal to the unit 50. The units 49, 50, and 51 comprise a circuitfor developing an M -Y correction signal where M represents adot-sequential type of brightness signal and Y represents aconstant-luminance type of luminance signal, such circuit being morefully described hereinafter and in applicants copending applicationSerial No. 339,145, entitled Color-Television Receiver.

Description of circuit details of units of the image-reproducingapparatus 13 of FIG. 1 as represented by FIG. 1b

Having described the combination of units comprising theimage-reproducing apparatus 13 of FIG. 1, the circuit details of oneembodiment of such apparatus will now be considered with reference toFIG. 1b. To correlate the units of FIGS. l and 1b, the numeralsdesignating the units of lFIG. 1 are utilized to designate dashed lineboxes representing the corresponding units in FIG. lb.

In the embodiment of FIG. 1b, the video-frequency amplier 28 comprises apentode 60 having the control electrode thereof coupled through avoltage divider 61 to the pair of input terminals 25, 25 and the cathodethereof coupled through a saturation control circuit to ground. Thesaturation control circuit includes a load resistor 62 and aparallel-tuned circuit 63, resonant at approximately 3.6 megacycles,connected in series between the cathode and ground and in parallel witha seriesconnected circuit of a condenser 64, an inductor 65, and atapped portion of an adjustable resistor 66. The condenser 64 andinductor 65 comprise a series-tuned circuit resonant at approximately3.6 megacycles. Ihe anode of the tube 60 is coupled through the delayline 40 and the filter network 41 to a source of potential +B. Thenetwork 41 includes in series a parallel-tuned circuit 67 and a resistor68, the circuit 67 being proportioned to effect peaking for the higherfrequency signals of the 0-4.2 megacycle band. The anode of the tube 61)is also coupled through the delay line 4i) and a condenser 69 inthenetwork 41 to the intensity `control electrode of the picture tube 30,the direct-current restorer 42 being shunted across the input circuit tosuch control electrode.

A condenser 70 and resistor 71 coupled in series between the anode ofthe tube 60 and ground, and with the junction of such elements connectedto the control electrode of a tube 72 in the modulator 44, comprise aconventional filter network 43 proportioned to translate substantially a3.0-4.2 megacycle signal to such electrode. The control electrode ofsuch tube is also coupled through a pair of series-connected couplingcondensers 73 and 74 to the anode of a tube 75 which is included in thethird harmonic amplifier 46. The cathode of the tube 72 is connected toground while the anode thereof is connected through a load resistor 78to a source of potential +B', is further connected through aseries-tuned circuit resonant at 10.8 megacycles to ground and throughthe band-pass or 6.6-7.8 megacycle filter network 4S to the cathode ofthe picture tube 30. A parallel-resonant circuit 79 in the network 45 isbroadly tuned to approximately 7.2 megacycles and is conductivelycoupled to a voltage divider 80 connected between the source ofpotential +B and ground, the latter divider comprising a brightnesscontrol for applying a unidirectional potential to the cathode of thetube 30.

The anode circuit of the tube 75 in the third harmonic amplifier 46includes parallel-tuned load circuits 76 and 77 resonant at the thirdharmonic of the aforesaid 3.6 megacycle signal developed in the outputcircuit of the push-pull amplifier 35. The cathode of the tube 75 isconnected to ground and the control electrode thereof is coupled througha coupling condenser 81 to an output circuit of the push-pull amplifier35. To obtain tripling of the 3.6 megacycle signal applied to thecontrol electrode of the tube 75, a properly proportioned biasedresistor 82 is coupled between the control electrode and ground. Theanode circuit of the tube 75 is also coupled to the second harmonicamplifier 47, specifically, through a coupling condenser 83 in the unit47 to the control electrode of a triode 84 therein. The anode of thetriode 84 is coupled to the screen electrode of the picture tube 30 andthrough a parallel-tuned circuit 85, resonant at approximately 21.6megacycles, to a source of potential +B while the cathode of the triode84 is coupled through the switch 48 to ground.

An output circuit of the push-pull amplifier 35 is also connectedthrough the phase-adjusting circuit 49, specifically, through a pair ofseries-connected coupling condeusers 86 and 87 in the unit 49 to thecontrol electrode of a triode 88 in the synchronous detector 50. Thephase-adjusting circuit 49 also includes a parallel-tuned circuit 89resonant at approximately 3.6 megacycles and coupled between thejunction of the condensers 86 and 87 and ground. The control electrodeof the triode 88 is also coupled through a high-pass filter network 43ato' the anode circuit of the amplifier 28 and the anode thereof iscoupled through the low-pass lter network S1 to the filter network 41.

Explanation of operation of image-reproducing apparatus 13 of FIGS. 1and 1b mental area'of an image and the single-gun tube, such asrepresented in FIGS. 1 and 1b and which sequentially reproduces suchcomponent colors. The NTSC signal, though not limited to utilizationwith apparatus for simultaneously reproducing component colors, readilylends itself to such utilization as described in the aforementionedElectronics article. This facility of utilization arises from theemployment of color-signal deriving apparatus external to the picturetube and separate channels for applying the different color signals tothe picture tube. However, when sequential reproduction of the componentcolors in an elemental area of the image is employed as in thesingle-gun picture tube considered herein, the primary colors arereproduced in some time order, or in other Words, in some time sequenceby the one electron beam. In employing such operation, it is axiomaticthat as the beam sequentially excites the different phosphors toreproduce the different colors, the signal representing the colors ofthe image to be reproduced applied to an intensity control electrode inthe picture tube should sequentially include color informaanca-olie tionin phase with the sequence of the colors being reproduced by means ofthe beam. If such color information is not inciuded in the appliedsignal in proper timing with the development of the, different colors bythe beam, then at least the colors in the image being reproduced do notcorrespond to the colors of the televised image.

A consideration of FIG. 1c will yassist in understanding the type ofcooperation required in a tube such as the tube 30 of FIG. 1 between thesignal which intensitymodulates the electron beam and the mpinging ofthe electron beam on the different phosphors. The phosphor Stripsrepresented in FIG. ic comprise a portion of the total area of the imagescreen 31 of the picture tube 30 and reproduce, when excited by theelectron beam, the colors indicated, the letters G, R, and Brepresenting the colors green, red, `and blue, respectively. Actuallythe representation of FIG. 1c is incomplete since conductors of the grid33 in the tube 30 of FIG. 1b should be represented as horizontal wiresspaced above the phosphors in the plane of the paper and verticallyalined on the R and B phosphors. For simplicity of representation suchconductors are not shown but are assumed to be present. in the apparatusi3 of FIG. 1b, a 3.6 megacycle colorswitching signal is applied by theoutput circuit of the amplier 35 to the two sets of conductors of thegrid 33 ofthe picture tube 30 causing the electron beam to trace a pathsuch as represented by the sine wave in FIG. 1c during each cycle ofsuch applied signal and along a fraction of each horizontal line ofscan. That is, if it is assumed that the cycle starts in the lower leftportion of a phosphor G, the beam first develops a green light, next ared light, again a green light, and finally a blue light during the onecycle. The sequence of colors reproduced during this one cycle is GRGB,includes green twice and repeats at a 3.6 megacycle rate Ialong eachline of scan. This means that if the 3.6 megacycle subcarrier wavesignal modulated by the color information in the manner previouslyco-nsidered herein is in phase with the 3.6 megacycle color-switchingsignal Iapplied to the grid 33 and which causes the beam to trace thepath represented in FIG. 1c and such modulated subcarrier wave signal isdirectly applied to an intensity control electrode of the beam, thensuch subcarrier wave signal should include in each cycle thereof colorAinformation such that during an initial small angle of the cycle theinformation would represent green, during a wider angle of the cycle theinformation would represent red, during another small angle it wouldrepresent green, and finally during another wide angle it wouldrepresent blue. The NTSC type of subcarrier wave signal does not includecolor information in such sequence or with such phase-anglerelationships. Therefore, in order to utilize the NTSC subcarrier Wavesignal with a picture tube such 'as the tube 30 the wave signal shouldbe modified. The unit 13 of FIG. 1b effects such modification. Thedegree and type of such modification will be better understood byinitially considering the composition of the NTSC signal and of acomparative dot-sequential type of signal which may be utilized with thetube 30 of FIG. lb without modification.

Referring -now to FIGS. 1d and 1e, the solid straight ylines in FIG. 1drepresent the vector relationship of the green, red, and blue colorcomponents in a cycle of an NTSC type of subcarrier wave signal.Similarly, the solid straight lines in FIG. le represent the vectorrelationship of similar components in ya dot-sequential type of signalsuch as described in General Description of Receivers for theDot-Sequential Colo-r Television System Which Employ Direct-ViewTri-Color Kinescopes in the RCAk Review for lune 1950. It is apparentthat the co-lor components in the NTSC type of color-television signalare not symmetrically disposed in phase with relation to each other in`a cycle of the subcarrier wave signal and are also not equal inintensity whereas the corresponding components in the dot-sequentialtype of signalv are symmetricall-y disposed at intervals of 120 in phaseand are equal in intensity. If ya dot-sequential 4type of signal isapplied to an intensity control electrode of the picture tube 30 so thatthe green component thereon is in phase with the initial green componentin the trace of the electron beam through one cycle fas represented byFIG. 1c, then, by employing a gating-signal for the beam, the beam maybe made to excite the phosphors at intervals along each cycle of trace.The portions of the phosphors excited during the gating periods a/rerepresented by the circles positioned along the sine wave in FIG. 1c. Byproper phasing of the gating signal, the 3.6 megacycle signalcontrolling the positioning of the beam on the image lscreen and thedot-sequential signal applied to an intensity control electrode of thetube, the green, red, and blue phosphors can be excited in phase withthe green, red, and blue components symmetrically disposed on a cycle ofthe applied dot-sequential type of subcarrier wave signal. However, suchgating cannot be employed with the NTSC signal to give high-fidelitycolor reproduction since, as represented by FIG. 1d, the colorcomponents are not at 120 phase intervals or of equal intensity.However, an NTSC signal may be modified Vso as to be similar to adot-sequential signal, and thus be suitable yfor use with the tube 30 ofFIG. 1b.

One form of apparatus formodifying an NTSC type of signal so that it isthe equivalent of aV dot-sequential signal and therefore suitable foruse with the tube 30, provided properly phased third harmonic gating ofthe modified signal is employed, has been described in theabove-mentioned copending application Serial No. 339,- 145. Tounderstand such modification it is is helpful to define the compositionsof the NTSC yand dot-sequential signals.

The monochrome or brightness component Y in the NTSC signal is definedas'follows:

whereas the corresponding component M of a dot-sequential signal isdefined as follows: Y

The chrominance or modulated subcarrier wave signal of the NTSC signalmay be defined in terms of its quadrature modulation components as R-Y/1.14 and B -Y/ 2.03. The latter components Iare representative of thered and blue color-difference signals, respectively, and are representedby the dashed line Vectors of FIG. ld. The subcarrier Wave signal mayalso be defined by the aforementioned G, R, and B modulation componentsthereof represented by the solid line Vectors of FIG. ld. In a similarmanner, the modulated subcarrier wave signal of a dot-sequential type ofsignal may be defined in terms of the three color components G, R, and Brepresented by the solid line vectors of FIG. le or may be defined interms of the quadrature modul-ation components .89 (R-Y) and .74(B-Y)represented by the dashed line vectors thereof.

In the apparatus described in the copending application Serial No.339,145, the brightness signal Y, defined by Equation 1 above, ismodified to be the equivalent of the brightness signal M, defined byEquation 2, above, by deriving a luminance correction signal M -Y fromthe modulated subcarrier Wave signal. The phaseadjusting circuit 49, thesynchronous detector 50, and the lter network 51 in FIG. 1b operate toderive such correction signal for combination with the signal Y inVplied thereto from the amplifier 35 so it has such an angle of 19 withrespect tothe modulated subcarrier v'vave and the latter wave signalheterodynes with the phase-adjusted reference signal in the unit 50 toderive the M-Y signal. For proper modification of the signal `Y thederived M-Y signal should have an intensity of approximately .58 withrespect to the intensity of the signal Y when they are combined and theunits 50, 51, and 41 are proportioned to effect the requiredattenuation.

In the apparatus described in the copending application Serial No.339,145, the NTSC type of subcarrier wave signal is also modified to besimilar to the dotsequential type of wave signal. As described in suchapplication, the modulated NTSC type of subcarrier wave signal isheterodyned with a second harmonic reference wave signal, properlyadjusted in phase and intensity with respect to the modulated NTSCsignal, to develop a dot-sequential type of 3.6 megacycle modulated wavesignal. In other words the heterodyning of the fundamental and secondharmonic signals effectively causes the vectors R-Y/l.l4 and B-Y/2.03 ofFIG ld to be modified in relative intensity so they are the equivalentof the vectors .89(R-Y) and .74(B-Y), respectively, of FIG le on theresultant 3.6 megacycle wave signal. The phasing and intensity of thesecond harmonic signal are such as to effect the desired increase in themagnitude of the B-Y vector relative to the R-Y vector. The phasing ofthe modified signals becomes that of the RY and B-Y signals if a newreference phase is employed.

Such modification of the NTSC signal so that it is the equivalent of adot-sequential signal, as described in the copending application SerialNo. 339,145, does provide a modified NTSC signal suitable for use with apicture tube such as the tube 30 of FIG lb. The conversion of Y to Mdoes not destroy the constant-luminance characteristic of Y since themodification can be considered as a luminance correction of the Y signalto cause the modified Y signal to cancel the luminance changes whichwould otherwise result from the modulated subcarr-ier when utilized inthe single-gun tube. However, such correction is only a first order onesince the gamma of the picture tube and other nonlinearsignal-translating characteristics of the different channels have notbeen considered. The modification of the NTSC subcarrier wave signalresults in colorimetric reproduction equivalent to that available withthe aforementioned three-gun tube. However, the utilization of thirdharmonic gating tends to decrease the efficiency of reproduction becausethe phosphors are only excited by the beam during the short gatingintervals with a maximum of a fifty percent duty cycle. In addition, theexciting of a small area of each phosphor at a 3.6 megacycle rate tendsto develop undesired crawling patterns in the reproduced image. It ispreferable that the beam should not be gated so that all of the beamenergy is employed in exciting the phosphors. The apparatus 13 of FIG.1b effects such result in a manner now to be explained.

Initially in explaining the operation of the apparatus 13 of FIG. lb inmodifying the NTSC signal so that it may be utilized with the picturetube 30, it will be helpful to consider again the sine-wave path of thebeam as represented in FIG. 1c. To simplify the explanation of themanner in which gating may be dispensed with it is helpful to explainfirst what happens as the width of the gates is increased and thendeduce from the results obtained what occurs as such gates overlap. Itis helpful in considering the gate widening first to assume that thegating frequency is double so as to occur at 60 intervals, and then notewhat occurs as two adjacent such gates are made into one. When gating at60 intervals, the phosphors will be excited in the sequence GRRGBBduring the cycle as represented by the combination of the dashed lineand solid line circles in FIG. 1c, and, if two cycles are considered,this sequence becomes GRRGBBGRRGBB. In the latter two-cycle path, if asequence is assumed to start with the second R, then a complete sequenceis RGBBGR and this sequence is cyclically repeated at the 3.6 megacyclefrequency of the color-switching signal applied to the grid structure33. It should be noted that in such sequence there are two reversedsequences, namely, RGB and BGR. Use is made of this relation indeveloping a modified NTSC signal to be used without gating.

The composite effect resulting from the combination of the one samplingeffected by the gating signal at one 60 point and the signal applied toan intensity control electrode of such tube may be considered as aresultant heterodyne signal and such combining or heterodyning operationmay be analyzed in terms of a Fourier series. If the `applied subcarrierwave signal is designated E and the components of the sampling pulse isdefined as a composite signal S, the signal S may be defined as follows:

and the resultant heterodyne signal H caused by the combination of thepulse sample and the signal E is then defined as follows:

In the above equations, the ms represent intensity factors and the 0srepresent the relative phase relations. In Equation 4, the first termindicates that the applied signal E is directly translated with unitygain, the second term indicates that synchronous detection of theapplied signal E occurs lat the fundamental sampling frequency with again of m1 and at a phase angle of 01 .'ith respect to the referenceangle of the cosine function, and the third term indicates thatsynchronous detection of the applied signal E occurs at the secondharmonic sampling frequency with a gain of m2 and at a phase angle of02.

Relating this analysis to a sampling operation which includes gating at60 intervals as previously discussed, the eect of each such sampling isto translate the monochrome or brightness signal, synchronously todetect any signal at the fundamental sampling or color-switchingfrequency into six components as represented by the vectors of FIG. 1f,and synchronously to detect any signal which is a second harmonic of thesampling frequency into three components for each cycle of the secondharmonic signal, or six components for each cycle of the samplingsignal, the latter six components being represented by FIG. lg.

In considering the vectors of FIG. 1f, it should be noted that the 60gating causes the aforementioned sequence of colors GRRGBB, as indicatedby the subscripts of the letters representing the colors, to beobtained. However, in FIG. 1g where the second harmonic signal is beinggated at 60 intervals of a fundamental signal, the gating is actuallygating on two cycles of the second harmonic signal and results in thesame color sequence GRRGBB but with only the green components at thesame phase in both cycles of the second harmonic signal. The red andblue components are interchanged in the two cycles.

In the vector diagrams of FIGS. 1f and 1g, the detection action of thetube for green is assumed to be at a phase angle of 90, that is, it isassumed to be in phase with a cosine function, or, in other words, thecolorswitching signal is a sine wave at 0 phase and may be representedas a vector at 0, and the gating signal is assumed to be symmetrical sothat 02:201 for each sampling operation. Considering FIGS. lh and lk, itshould be noted that the net detection action resulting from theexcitation of the red and blue phosphors at the fundamental frequencyare equal and opposite along the 0 axis and that the net detectionaction for green resulting from sampling at the fundamental frequency is0.

Thef'vectors of FIG'. lh represent such resultant detection action andit should be noted that the resultants R and B, because of thetrigonometric relations of the B5, B6 and R2, R3 vectors in FIG. 1f,have magnitudes of 2 .866m1. In considering the gating of the secondharmonic signal, the net red and blue signals are equal and at 270 phasewhile the net green signal is equal to twice the red or blue signalsderived and is at 90 phase. The vectors of FIG. lk represent suchrelationship, the B and R vectors being represented as being displacedfrom the origin for simplicity of representation. Actually such vectorsshould be represented in coincidence in angular position.

From an analysis of the above, it then follows that, when employingsixth harmonic gating, effectively derivation of the color signalsoccurs only along one axis, that is, the -180 axis with respect to thefundamental subcarrier wave-signal frequency and along only one axis,that is, the 90-270or axis with respect to a second harmonic subcarrierwave signal. In other words, if the NTSC subcarrier wave signal isdirectly utilized in combinationl with sixth harmonic gating in whichthe colorswitching frequency is equal to the mean frequency of the NTSCsubcarrier wave signal only a two-color picture should result. That is,as represented by FIG. lh, there should be no derivation of signalsrepresentative of green. Inorder to derive the green components, thesecond harmonic of the NTSC subcarrier Wave signal should also beapplied to the picture tube. Actually, since the operation of asingle-gun picture tube is nonlinear in that it has some gamma, somedetection of the signals representative of green from the fundamentalNTSC subcarrier wave signal does result though such detection is notphase sensitive and consequently a desaturated green would be reproducedregardless of the phase direction of the green component along the909-270 axis. However, the nonlinear signal derivation results justconsidered may be ignored if a relatively simple modifying apparatus isdesired in which the results of such nonlinear signal derivation areminimized.

If it be assumed that the effective sampling operation effected in thetube 30 of FIG. 1b has fundamental and second harmonic components ofamplitudes Zml and 21112, respectively, relative to a unidirectionalcomponent of unity, as previously discussed herein with reference toEquations 3 and 4, then by analyzing the vector diagrams of FIGS. lh andlk, the first order solution of the colorsignal detection efficiency inthe tube can be evaluated for each primary color. The results of suchanalysis are tabulated below and are expressed in such table in relationto an arbitrary selection of unity translation for the monochromecomponent. In other words, all of the vector magnitudes represented inFIGS. lh and 1k have been divided by two since the monochrometranslation, previously considered as being uni-ty for one sampling, foreach pair of green, red, or blue samples is two.

Mono- Fundamental Second Harmonic Primary Color chrome Componentl CosineSine Cosine Sine 1 0 0 mz 0 1 0 866ml 5mg 0 l 0 .866m1 5m O 14 If it beassumed that the` desired green, red', and blue output signals resultingfrom the decoding operation in the single-gun tube are G, R, and B,respectively, the resulting equations may be solved for M, al, and a2with the following results:

From the above, it follows that, as far as .first order effects areconcerned, correct coloirimetric reproduction is obtainable when using asingle-gun picture tube such as tube 30 of FIG. lb if the monochromecomponent, the fundamental-frequency sine component, .and the secondharmonic cosine component are as defined by the latter three equations,respectively. As Afar as; such first order effects are concerned, itshould be noted that the fundamental-frequency cosine component and thesecond harmonic sine component may have any magnitude since they areaveraged out in the decoding operation as indicated by the lack ofvectors for such components in FIGS. lh and 1k.

To summarize the latter portion of the above consideration, it may bestated that the NTSC signal may be -modied for utilization in asingle-gun tube such as the tube 30= of FIG. lb to effect acceptablecolorimetric reproduction of a televised image provided four operationsare performedl with respect to such signal. 'The rst of these is theutilization of a converter such as described in the aforesaid copendingapplication Serial No. 339,145 andV previously considered herein asbeing represented by the units 49, 50, and S1 of FIG. lb for convertingthe brightness signal Y to the dot-sequential type of brightness` signalM. Secondly, the mean frequency of the NTSC sub-carrier Wave signalapplied to an intensity control electrode of the picture tube and thefrequency of the color-switching signal applied to the gridv structure33` thereof should be equal and, as indicated by Equation 9, thecomponent of the NTSC sub'- carrier wave' signal along the R-B.modulation axis thereof should be in phase with the sine component ofthe color-switchingl signal. Next, the NTSC subcarrier wave signalshould be heterodyned with either a fundamental or third harmonic signalto develop a modulated second harmonic subcarrier wave signal and t'helatter should be applied to the intensity control electrode of thepicture tube so that the modulation axis along which the G-.SR-.SBcomponent thereof occurs is in phase with the cosine component of thecolor-switching signal'. Finally, the amplitudes of the modulatedfundamental and second harmonic -wave signals should be proportioned solthat the correct color saturation is olbtained. Such proportioning is afunction of the effective width of the gating angle which determines themagnitudes of the constants m1 and m2. The apparatus 13 of FIG. 1b isdesigned to perform the four operations just discussed.

Preliminary to= considering the manner in which the apparatus 13 of FIG.1b performs the four operations just mentioned, it will be helpful inunderstanding the operation of the -unit 13 to explain more fully thephase relations of the fundamental and second harmonic subcarrier wavesignals with respect to the color-switching signal. Since the modulationaxes R-B and G-.SR-.SB are essential to such consideration, it willinitially be helpful to locate such axes on a vector diagram of thefundamental and second harmonic wave signals. FIG. 1m represents suchvector diagram lindicating that the modulation axis R-B is 209 and theG-.SR-.SB axis is both clockwise from the B-Y reference axis at 0.Referring now to FIG. 1c,if the color-switching signal develops thetrace cycle represented therein, then the R-B axis of the appliedfundamental subcarrier wave signal is iny phase with the colorswitchingsignal and the peak of the signal on the G-.SR-.SB axis of the secondharmonic signal should occur as the color-switching signal directs thebeam onto the green phosphor. The relationship of the fundamental secondharmonic and the excitation of the phosphors by a sixth harmonic gatingsignal is represented by FIG. 1n. Curve F in this ligure represents onecycle of the fundamental subcarrier wave signal as applied to thepicture tube 30, curve S represents two cycles of the second harmonic ofsuch wave signal, and curve C represents the resultant or compositesignal developed from the combination of the fundamental and second`harmonic signals. The line M represents the monochrome or brightnesssignal. In considering FIG. ln reference Should also be made to FIG. lcand particularly to the six samples represented therein. These samplesare represented by the vertical lines GRRGBB of FIG. 1n. It should benoted that the net primary colors for each sample during each of the sixgatings is obtained from an average of the fundamental and secondharmonic signals modulating the beam during the interval of such sample.The components which are in quadrature during each sample are ofopposite sign and thus cancel. The signal relationships represented byFIG. 1n are of the desired type wherein any quadrature components arenot present since they cause opposite polarity eiects and thus averageout over a color-switching cycle. Actually such relationships are notcompletely developed in the system of FIG. 1 because for reasonsdiscussed above the quadrature components may cause some effects in thesystem of PIG. l. However, a system described hereinafter with respectto FIG. 4 does fully develop the signal relationships represented byFIG. 1n.

In FIG. 1b the composite NTSC signal including both the brightnesssignal Y and the modulated subcarrier wave signal is applied through thepair of terminals 25, 25 and the gain-control resistor 61 to thecontrol-electrode circuit of the tube 6i). The cathode circuit of suchtube controls the intensity of the modulated subcarrier wave signal withrespect to that of the wide band brightness signal so that proper colorsaturation may be obtained. Such color saturation is determined by therelative intensities of the brightness and chromaticity signals. Theseries-resonant network of the condenser 64 and inductor 65 tends toshunt the subcarrier wave signal with respect to the brightness signal,thereby decreasing the degeneration in the cathode circuit andincreasing the intensity of such wave signal while the parallel network63 tends to block translation of the wave signal, thereby decreasing thegain thereof with respect to the brightness signal. The variableresistor 66 combines these opposing effects in the proper proportions tocontrol the relative intensities of the subcarrier wave signal and thebrightness signal and thereby to control color saturation.

The composite NTSC signal including the brightness signal andfundamental subcarrier wave signal developed in the output circuit ofthe amplifier 28 is translated through the delay line 40, the -4.2megacycle filter network 41, and the direct-current potential thereof isrestored by the unit 42 prior to application to the intensitycontrol-electrode circuit of the picture tube 30. The delay line isproportioned to effect the same time of travel for signals through theunits 40, 41, and 42 as is required to translate the chrominance signalsthrough the other channels in the image-reproducing system. Aspreviously explained `herein, in order to modify the translatedbrightness signal so that it is converted to a signal M suitable forutilization with the single-gun picture tube 30, the modulatedsubcarrier wave signal with side bands between 3.0 and 4.2 megacycles istranslated through the filter network 43a and applied to thecontrolelectrode circuit of the triode 88 in the synchronous detector G.A 3.6 megacycle reference signal developed in the output circuit of thepush-pull amplifier 35 is translated through the phase-adjusting circuit49 and applied after phase adjustment to the control-electrode circuitof the triode 88. The M -Y correction signal is derived by synchronouslydetecting in unit 50 the NTSCsubcarrier wave signal at an angle of -{-l9counterclockwise where the B-Y axis of modulation is considered 0. Thephase-adjusting circuit 49 eiects such control of the 3.6 megacyclesignal translated therethrough so that the reference signal effectssynchronous detection in the unit 500i that component of the subcarrierwave signal applied by the unit 43 at the 19 phase point thereof. Thedetected signal, or M--Y correction signal, is developed in the anodecircuit of triode S8. The theory and details of such operation are morefully described in the copending application Serial No. 339,145. The0O.6 megacycle band of such correction signal is translated through thelow-pass filter network 51 and combined with the Y signal in the network41 to develop the desired M signal.

As previously discussed, the fundamental NTSC subcarrier wave signaltranslated through the units 40, 41, and 42 and applied to thecontrol-electrode circuit of the picture tube 30 should have apredetermined phase with respect to the color-switching signal developedfrom the reference signal in the output circuit of the push-pullamplifier 35 and applied to the grid structure 33 of the picture tube30.` More specifically, it is desired that the color-switching signal bein phase with the R-B axis of the translated NTSC subcarrier wavesignal. Conventional phase control of the signal developed in theamplifier 35 may be utilized to control the timing of thecolor-switching signal as applied to the grid structure 33 to effectsuch phase relation. If desired such control may be effected inthegenerator 21 of FIG. l.

Finally, the amplified subcarrier wave signal developed in the outputcircuit of the unit 28 is translated through the 3.0-4.2 megacyclefilter network 43 and applied to the control electrode of the modulatortube 72. The reference 3.6 megacycle signal developed in the outputcircuit of the push-pull amplifier 35 and which is phase-controlled withrespect to the NTSC subcarrier wave signal by the units 19, 20, and 21of FIG. 1 is applied to the third harmonic amplifier 46 for developing a10.8 megacycle signal therefrom. The latter signal is applied to thecontrol electrode of the tube 72 of modulator 44 to heterodyne with theNTSC subcarrier wave signal also applied thereto to develop a modulatedsecond harmonic or 7.2 megacycle subcarrier wave signal in the outputcircuit of the unit 44. The series-resonant circuit coupled to the anodeof the tube 72 shunts the 10.8 megacycle signal incidentally developedin the output circuit of such tube. The second harmonic signal is thentranslated through the 6.6-7.8 megacycle filter network 45 wherein it ismodified in phase so that it has such phase relation to the 3.6megacycle color-switching signal applied to the grid structure 33 of thepicture tube 3) that the phase axis of the modified subcarrier wavesignal along which G-.SR-.SB component occurs is in quadrature phasewith the color-switching signal. More specifically, the phase of thesecond harmonic signal is so adjusted that the peak of the signal on theG-.SR-.SB axis thereof which, as represented by FIG. 1m, is at +140 withrespect to the B-Y referenceaxis, occurs in coincidence with thedirecting of the beam on the green phosphor by the color-switchingsignal.

The 3.6 megacycle color-switching signal applied to the grid structure33 by the amplifier 35 and the transformer 34 causes the electron beamto trace a sine-wave path, such as represented by the Sine wave in FIG.lc, along each horizontal line. The brightness signal and fundamentalsubcarrier wave signal applied to the controlelectrode circuit of thepicture tube 30 and the second harmonic subcarrier wave signal appliedto the cathode circuit thereof moduate the intensity of the electronbeam. As explained above, such modulation in cooperaccenni ation withlthe color switching of the beam efects the excitation of the primarycolors in accordance with the primary color information on the appliedsubcarriers and the televised color image is reproduced; For reasonsexplained' more fully hereinafter, sixth harmonic gating of the electronbeam, which may be effected by means of the 21.6 megacycle signalapplied to the screen electrode of the tube 30 by the amplifier 47, neednot be employed. If employed, the positive peaks of they gating signalshould occur at 60 intervals of the colorswitching signal.` Suchvphasing may rbe controlled by the proportioning of the conventionalelements in the amplifier 47.

In describing the development of the modiiied NTSC signal considerationhas not been given to maintaining the relative intensities of thechominance and luminance components, which are in the unmodilied NTSCsignal developed in the output circuit of the ampliiier 28, and in themodified NTSC signal developed for application to the control-electrodecircuit of the picture tube 30. If such relative intensities are to bemaintained, and such is desirable for more faithfulV reproduction of thetelevised image, then, if the gain in the channel including the filternetwork 41 isassumed to be unity for the luminance signal, thecomponents along the R-B and G-.5R-.5B axes should, respectively, havethe magnitudes .43(R--B) and .56(G-.5R--.5B). If narrow angle sixthharmonic gating is employed and thus ml=m2=1,`then the filter network 41or, if desired, the amplifier 28, should be proportional to giveapproximately a relative gain of 1.35 for the subcarrier wave signal andits side bands and the gain in the channel including the units 44 and 45should be adjusted to be 1.2 times the unity gain for the luminancesignal.

As stated above, the system 13 of FIG. l may be operated without sixthharmonic gating. When no gating is employed, the two areas of the redphosphor excited when such gating is employed merge and effectivelybecome one 120 area. The blue areas similarly merge into one 120 areaWhile the green areas become two 60 areas. If only first order effectsare considered, since the positions of the vectors of FIGS. lh and 1k donot change as the gating duration isincreased or when gating is notemployed, theoretically no color errors should occur and the phosphorsyshould be excited one hundred percent of the time. The values of m1 andm2 would change since for the 60 gates which are effectively present asthe color switching traces two 60 paths through each of the green, red,and blue phosphors the intensity of the signal would be averaged overthe interval of the gate. It has been fou-nd that when noy gating signalis employed, m1 is reduced from unity to .96 and m2 from unity to`.83.Thus the luminance and chrominance channel gains would change-from 1.35and 1.2 to 1.41 and 1.44, respectively, when no gating is employed.

l t should' be noted that second and higher order effects would tend tocause some color contamination as gating is dispensed with, such colordistortion being caused by the development of components from thesignals along the 90270 vector axis in FIG. Ik and alon'gthe 0-l80vector axis in FIG. lh. However', the nonlinear signaltranslating'characteristic of the electron beam in the tube 30 tends to reduce suchcolor contamination since the gamma of the tube tends to cause lessresponse to lowinteusity signals and much higher response to signals ofgreater magnitude thus tending to develop a signal-sharpening effectwhich correspond'sto the effect of a narrow gating pulse. As a result,the system13 of FIGS. l and' lb does not need a sixth harmonic gatingsignal su'ch as developed by the amplifier 47 and 'the electron beam inthe picture tube 30 may be` continuously applied to the image screenwith an intensity controlled onlyby the applied luminance andchrominance signals. l* Such operation of the single-gun picture tubeapproximatelysimulates the simultaneous operation of the three-gun tubesince, though: a 3.6 megacycle color-switching; signal is employed, thegreen phosphor is excited at a' 7.2 megacycle rate, being excited twicein each 3.6 megacycle cycle. This results in the reproduction ofsubstantially the equivalent of a simultaneous green image which has a7.2 megacycle pattern invisible for all practical purposes. Since theeye has less acuity for red and blue detail in the composite picture,the 3.6 megacycle patterns in such colors have relatively minor eflectsin the composite color image. Consequently, the composite image is, forall practical purposes, the equivalent of a simultaneous image.

To summarize the operation of the image-reproducing apparatus 13 of FIG.1b, a conventional NTSC type of signal including both monochrome andmodulated subcarrier Wave-signal components is applied to the amplifier28, wherein saturation control of the subcarrier wave signal iseffected, and developed in the output circuit of such amplifier. Theluminance and subcarrier wavesignal components comprising the compositeNTSC signal are translated through the units 40, 41, and 42, theluminance signal being modified in the unit 41 by an M Y correctionsignal derived in the synchronous detector 50 and applied as alow-frequency signal to the filter network 41. A properly phasedcolor-switching signal is developed by the amplifier 35 and appliedthrough the transformer' 34 to the grid structure 33 of the tube 30 todirect the electron beam therein on the diiterent phosphor strips of theimage screen 31 thereof in a cyclic manner such as represented by FIG.lc but with no gating of the beam. A modulated second harmonicsubcarrier wave signal properly phased and controlled in intensity isdeveloped in the unit 44 and applied through the bandpass filter network45 to the cathode of the picture tube Sti. If desired, sixth harmonicsampling may be effected by applying a signal developed in the outputcircuit of the unit 47 to the screen electrode of the picture tube 30.kThus, there is developed inthe control electrode-cathode circuit of thepicture tube 30 a modified NTSC type of signal such as previouslydiscussed herein and which will combine with the colorswitching signalapplied to the grid structure 33 to reproduce a televised color image.

Description of image-reproducing system of FIG. 2

As discussed with reference to the system 13 of FIGS.y 1 and 1b, suchsystem is capable of effecting acceptable reproduction of a televisedcolor image as long as higher order signal-translation effects do notbecome so great as to be disturbing. ln other words, as previouslymentioned, the modification of the NTSC signal by means of the system 13of FIGS. 1 and 1b is effected only to compensate for rst order efiects,higher order nonlinear signal-translation effects being considered asnegligible. It may be desired to modify the NTSC signal in such manneras also to compensate at least to some degree for higher order effects.The system of FIG. 2 is designed to effect such result.

In the system of FlG. 2, since such system is similar in many respectsto that of FIGS. l and 1b, units which are the same in all such systemsare identified by the same reference numerals while units in the systemof FIG. 2 which are analogous to units in FIG. l are identified byemploying the reference numeral of the corresponding unit in FlG. l witha factor of'Z'adde'd thereto. Units and circuit elements in FIG. 2 whichare firstl described therein are identified by reference numeralsbetween 101 and 130.

The system 213 of FIG. 2 includes in the channel for translating theluminance signal a 0-3 megacycle filter network and a modified form ofdirect-current restorer 242. A tap on a potential divider 101 coupledbetween the source of potential -l-B and ground is connected to theanode of the diode in the direct-current restorer 242 andV the potentialdivider is utilized to effect brightness control to the output circuitof the restorer 242. The amplifier 102 comprises a pentode 103 havingthe anode circuit thereof coupled through a parallel-tuned circuit 104to a source of potential +B and also coupled to the screen electrode ofthe picture tube 30. The circuit 104 is resonant at approximately themean frequency of the subcarrier wave signal, that is, at 3.6megacycles. The cathode of the pentode 103 is coupled for unidirectionalsignals through an adjustable tap on a voltage divider 105 connectedbetween the source of potential +B and ground and utilized to adjust thebias on the cathode. The control-electrode circuit of the tube 103 isconnected to an intermediate terminal of a voltage divider 106 coupledbetween the output circuit of the direct-current restorer 242 andground. The divider 106 is proportioned to reduce the limits of thevoltage range of the signal applied to the tube 103 so such range iswithin the operating limits of such tube. The screen electrode of thetube 103 is connected to a source of screen-electrode potential +Sg andthe suppressor electrode thereof is coupled through a phase-adjustingcircuit 107 to the output circuit of the push-pull amplifier 235.

In the chrominance channels of the system of FIG. 2, an amplifier 243having a pass band of 3-4.2 megacycles is utilized in place of thefilter networks of FIGS. l and lb having a corresponding pass band. Inthe channel for developing the modified second harmonic signal, there isincluded a signal-sampling device 108 for effecting translation of onlythe modulated NTSC signal which corresponds with the G-.SR-.SB axispreviously discussed herein with reference to FIG. 1 while shunting outsubstantially all components along the axis in quadrature thereto. Thedevice 108 comprises a diode 109 having the anode circuit thereofcapacitively coupled to the output circuit of the amplifier 243 andcoupled through parallel-resonant circuit 110 to ground, the lattercircuit being tuned to approximately 3.6 megacycles. The anode of thetube 109 is also connected to an input circuit of the modulator 44 whilethe cathode thereof is coupled through a biasing circuit 111 in serieswith an inductor 112 to ground, the circuit 111 being proportioned tobias the cathode with respect to the anode of the tube 109 so thatconduction occurs through such tube for substantially only thoseintervals when the negative peak portions of the signal applied to thecathode occur. The junction of the circuit 111 and the inductor 112 iscapacitively coupled to the screen-electrode circuit of the push-pullamplifier 235 which includes a parallel-resonant circuit 113 fordeveloping the 7.2 megacycle signal. The parameters of the tuned circuit113 are so proportioned that the 7.2 megacycle signal applied to thecathode of the diode 109 has a positive peak during the interval theaforementioned G-.SR-.SB axis of the NTSC signal is being applied to theanode of the diode 109 and has a negative peak for the axis inquadrature thereto. The screen electrodes of the tubes in the amplifier23S are connected to the network 113 so that these tubes act aspush-push doublers for the 3.6 megacycle signal being translatedtherethrough.

The system of FIG. 2 also includes another signalsampling device 114including a. diode 115 having the cathode thereof capacitively coupledto the output circuit of the amplifier 243 and coupled to ground througha parallel-tuned circuit 116, resonant at 3.6 megacycles. The anode ofthe diode 115 is coupled through a biasing circuit 117 in series with aninductor 118 to ground, the circuit 117 being proportioned to bias theanode of the tube 115 with respect to the cathode thereof so that suchtube is conductive for narrow intervals when the positive peaks of the7.2 megacycle signal applied to the anode occur. The junction of thecircuit 117 and the choke 11S is coupled to the screen-electrode circuitof the amplifier 235 for applying the 7.2 megacycle signal to suchjunction. As with respect to the device 103, the parameters of the tunedcircuit 113 cause the 7.2 megacycle signal applied to the anode of thetube to have a definite phase with respect to the NTSC subcarrier wavesignal applied to the cathode thereof. More specifically, the phaserelation of the applied signals is such that the 7.2 megacycle signalapplied to the anode of the tube 115 has a negative peak during theinterval the R-B axis of the NTSC subcarrier wave signal is beingapplied to the cathode thereof.

The output circuit of the modulator 44 comprises a tuned circuit 245resonant at the second harmonic of the NTSC subcarrier Wave signal,specifically, at 7.2 megacycles. The tuned circuits 116 and 245 areinductively coupled to windings 121 and 122, respectively, which are inseries between a source of bias potential +C and the cathode of thepicture tube 30. The circuit including the tuned circuit 116 and theWinding 121 may have the parameters thereof proportioned to effect theproper phase relation between the fundamental NTSC subcarrier wavesignal translated therethrough and the color-switching signal applied tothe grid 33, as explained with reference to FIGS. 1 and 1b. However,other parameters may be adjusted, in a conventional manner, to effectsuch phase relation. Similarly, the parameters of the circuit 245 andthe winding 122 may be proportioned to effect the proper phase relationbetween the second harmonic subcarrier wave signal and thecolor-switching signal, as explained with reference to FIGS. 1 and 1b.

Explanation of operation of system of FIG. 2

As previously mentioned, the system of FIG. 2 minimizes the effect ofthe gamma of the picture tube and other nonlinear characteristics in thesignal-translating channels by effectively selecting in differentchannels only the color information along the previously discussed R-Baxis and the G-.SR-.SB axis of the 3.6 megacycle NTSC wave signal. Theneed for selecting only such axes is premised on the recognition thatthe color-deriving operation of the tube 30 of FIG. 1, when a modifiedNTSC signal is applied thereto as explained with reference to FIGS. 1and lb, because of the nonlinear signal transla tion in such tubederives not only those components in phase in the fundamental and secondharmonic signals but also tends to derive some color from the quadraturecomponents of these signals which are, as explained with reference toFIG. l, of opposite sign and equal intensity voltage-wise in twosuccessive derivations. As voltages such quadrature signals cancel eachother but optically they may not do so because of the gamma of thepicture tube. To eliminate such quadrature components prior toapplication of the fundamental and second harmonic subcarrier wavesignals to the picture tube, chrominance component-selection systemscomprising axis selectors as represented by the devices 108 and 114 ofFIG. 2 are employed. When such quadrature components are eliminated, thesignals in FIG. 1n then accurately represent the operation of thesystem.

To effect the desired axis selection the NTSC signal is applied by theamplifier 243 through a coupling condenser to the sampling device 114and the phasing of the 7.2 megacycle signal in the anode circuit of thediode 115 is such that it has a negative peak during each interval theR-B axis of the NTSC subcarrier wave signal is applied to the cathode ofthe diode 115. The diode 115 becomes conductive during the applicationthereto of the positive peaks of the 7.2 megacycle signal therebydamping out the components along the axis in quadrature with the R-Baxis. The R-B components on the cathode of the diode 115 during thenonconducting period of such-diode are developed across the turnedcircuit 116 and applied, with proper phasing, through the winding 121to'the cathode of the picture tube 30. The action of the diode 115 issuch as to effect translation of the components along the R-B axis ofthe applied NTSC signal while shunting substantially all components onthe axis in quadrature with the R-B axis. Thus the fundamental NTSC.signal applied to the tube. 30 effectively has only the components alongthe R-B axis represented. by the vectors in 1h and nonlinear effects inthe tube 30 cannot effect rectification or detection of components alonga quadrature axis since none of such quadrautre components is translatedand applied to the picture tube. Similarly, thesampling device 108,because of the previously described phasing of the NTSC wave signal and7.2 megacycle signal as applied to the diode 109, causes the fraction ofthe NTSC signal having components along the G-.SR-.SB axis to be appliedto the unit 44 while the device 108 effectively shunts the quadraturecomponents of such NTSC signal. Thus, referring to FIG. lk, only thedesired modulation components along the 90-270 axis are developed on thesecond harmonic. signal in the unit 44. This wave signal, properlyphased by the tuned circuit 24S and the winding 122 is also applied tothe cathode of the picture tube 30. The luminance signal translatedthrough the unit 241 and applied to the control electrode of the picturetube 3B, and the fundamental and second harmonic subcarrier wave signalsapplied to the cathode thereof combine in such tube to reproduce thecolor image in the manner described with reference to FIGS. l and 1b.However, the nonlinear signal-translating characteristics of the tube3i) can no longer cause color contamination by effecting undesiredderivations of improper color components at improper times, asexplainedwith reference to FIGS. l and 1b, and therefore the color fidelity ofthe system of FIG. 2 is higher than that of FIGS. l and lb.

The amplifier 102 in the system of FIG. 2 applies a 3.6 megacycle signalto the screen electrode of the picture tube 30 to effect balancing ofthe lights'emitted by the different phosphors so that such lights willcombine to reproduce the different shades of black and white over thetotal brightness range when a monochrome signal is being received and amonochrome image is' being reproduced. It is known that the phosphorsfor reproducing the different colors do notfdo so with equalefficiencies. For example, the phosphor for reproducing red is lessefficient than those for reproducing green and blue. To compensate forthis, the amplifier applies a 3.6` megacycle signal to the screenelectrode of the picture tube 30.50 that the positive peak thereofoccurs in coincidence with the impinging of the beam on the redphosphor. In this way the energy of the beam is increased during theinterval the beam is impinging on the red phosphor and compensation forthe inefliciency of the phosphor is effected. The network 107 modifiesthe phase of the signal-applied to the tube 103 so it is' applied withthe proper phase as described above. By means of the voltage divider 106and the bias control 11115 the tube 133 is adjusted to simulate thesignal-translating characteristics of the cathodecontrol electrodecircuit of the picture tube 3l). In other words, once a proper level forthe 3.6 megacycle signal developed in the anode of the tube 103 has beendetermined for some shade of brightness', the gain of the tube 103 isadjusted so as such shade changes the proper percentage change occurs inthe level of such signal to maintain the desired control. In this wayadjustments of the brightness control 161 and the direct-currentrestoration ac-tion of the restorer 242 not only adjust the potentialson the electrodes of the picture tube l301 to obtain the desiredbrightness levels but also effect a similar correction of the intensityof the 3.6 megacycle signal developed in the anode of the tube 103.

Description of image-reproducing system of FIG. 3

The image-reproducing system of FIG. 3 represents a modified form of theaxis-selector type of system described With reference to FIG. 2. Sincethe system of FIG. 3 includes many units which are similar-to units inthe systems of FIGS. l, lb, and 2, such units' are identified by thesame reference numerals. Units in the systemv of FIG. 3 which areanalogous to units of 22 FIGS. l or 1bl are identified by the referencenumerals of such analogous units with a factor of 300 added thereto.Units and elements first described in FIG. 3 are identified by numeralsinthe group 131-150.

In the system of FIG. 3, the direct-current restorer 342 includes abrightness control and is coupled to both the control electrode andcathode of the picture tube 30 to effecty direct-current restoration forthe signals on both electrodes since -i-n FIG. 3, the M-Y correctionsignal is` applied tothe cathode while the brightness signal is appliedto the control electrode. The circuit including the triode 131 comprisesa composite axis selector or sampling device for both the R-B and theG-.SR-.SB axes. ofV the NTSC subcarrier wave signal. The anode of thetriode 131 is coupled through a parallel-tuned circuit 132 to a sourceof potential -l-B and to the modulator 44. The cathode of the tube 131is coupled through -a series-resonant circuit comprising an inductor 133and a condenser 134 to the output circuit of the video-frequencylamplifier 28 and through an inductor 13851 and a resistor 138b, inseries, to ground. The parallel-resonant circuit 132 and theseries-resonant circuit 133, 134 are both resonant at approximately themean frequency of the subcarrier wave signal. The cathode of the tube131 is also coupled through a biasing resistor 135 to the controlelectrode o-f the tube 131. The latter electrode is connected through acondenser 136 to the screen-electrode circuit of the amplifier 23S, suchscreen-electrode circuit including the parallel-resonant circuit 113described with reference to FIG. 2 and resonant at the second harmonicof the mean frequency of the subcarrier wave signal, that is, at 7.2megacycles. The out-put circuit of the videoJfrequency amplifier 28 isalso connected through a resistor 139 to an input circuit of thesynchronous detector 5t).

The. output circuit of the push-pull amplifier 235 is capacitivelycoupled through-a capacitive voltage divider to. the screen electrodeofthe picture tube 30 to eiect color balance so that monochrome imagesmay be reproduced over the total brightness range.

Explanation of operation of system 0f FIG. 3

Except for the operation of the color-balancing circuit coupled to thescreen electrode of the picture tube 30 and of the axis selectorincluding the triode 131, the system of FIG. 3 operates substantially inthe manner explained with reference to the system of FIG. 1. However, inthe system of FIG. 3 no sixth harmonic gating circuit is coupled to thescreen electrode of the picture tube 3i? and thus no gating occurs and,since the directcurrent restorer circuit 342 is coupled to both thecathode and control electrode of the picture tube, direct-currentrestoration is effected for the luminance and luminance correctionsignals on these electrodes.

In considering the operation of the axis selector including the triode131, it is to be remembered that itis desired to apply a fundamentalNTSC subcarrier Wave signal including as modulation informationsubstantially only that color information along the R-B axis of the NTSCsubcarrier. wave signal developed in the output circuit of the amplifier28. It should also be remembered that the second harmonic modulated wavesignal developed `from the NTSC subcarrier wave signal applied from theoutput circuit of the amplifier 28 should include substantially thatinformation along the G-.SR-.SB axis of the latter NTSC subcarrier wavesignal. As indicated by the vector diagram of FIG. lm such informationeffectively occurs along yaxes which are at approximately an angle of70. It has been found that the signais on these axes can be consideredto be substantially out-of-phase with respect to each other or atsubstantially phase points of -a second harmonic of the subcarrier wavesignal. Therefore, the single triode 131 can operate in such manner asto perform the function of one of the diodes of FIG, 2 b 'y damping thecomponents on approximately the G.5R.5B axis out of the circuit fortranslating approximately the R-B axis and performs the function of theother diode by translating approximately the G.5R-.5B axis of themodulated subcarrier wave signal. In the manner explained with referenceto such diodes a properly phased 7.2 megacycle signal is developed inthe tuned circuit 113. This signal is applied to the control electrodeof the triode 131 to cause it to be conductive during short intervals atthe positive peaks of the 7.2 megacycle signal and to be otherwisenonconductive. When the triode 131 is conductive it translates theinformation on the cathode thereof to the anode thereof and applies suchinformation to the modulator 44. Thus, if the triode is renderedconductive during that period of time when approximately the G-.SR-.SBaxis of the NTSC subcarrier wave signal is on the cathode thereof, thenthe 3.6 megacycle NTSC subcarrier wave signal developed in the anodecircuit thereof is modulated substantially only by the components alongsuch axis. During the period of time the triode is conductive the 3.6megacycle signals in the output circuit of the amplifier 28 areeffectively shunted by such conduction and, therefore, no such signalsare translated through the delay line 40. Since the axis of the wavesignal occurring during such conduction is substantially in quadraturewith the R-B axis, only the R-B axis is translated through the delayline 40 for application to the control electrode of the tube 30. Thus,the fundamental and second harmonic of the chromaticity signal appliedto the cathode and control-electrode circuits of the tube 30 includesubstantially only the information along the desired axes as explainedwith reference to FIG. 2. As a result, the color contamination caused bythe previously considered higher order etfects are diminished.

The operation of the triode 131 in translating the G-.SR-.SB axis to theexclusion of its quadrature component may be analyzed mathematically todemonstrate that the variation of the triode conduction at the secondharmonic frequency of the subcarrier signal eectively derives subcarriersignal components of original phase sequence and subcarrier signalcomponents of reversed phase sequence including a given component ofsubstantially the same magnitude as and of opposite polarity to thecorresponding component of the derived subcarrier signal components oforiginal phase sequence for developing a resultant subcarrier signalrepresentative of a selected chrominance component along a given axis tothe substantial exclusion of its quadrature component. Such an analysisinvolves multiplying the over-al1 gain characteristic of the samplingdevice by the signal translated thereby to indicate that original phasesequence and -reversed phase sequence exist in the relations describedabove. This analysis is similar to that employed in application SerialNo. 339,145 in explaining the operation of the subcarrier modifier ofthat application.

The color balance eiected by the application of the 3.6 megacycle signalfrom the transformer 34 to the screen electrode of the picture tube 30is a simplified form of that described with reference to FIG. 2. Thereis no attempt in the system of FIG. 3 to correct the level of the 3.6megacycle signal for variations in brightness levels.

Description of image-reproducing system of FIG. 4

The image-reproducing system of FIG. 4 represents another modified formof the axis-selector type system initially described with reference toFIG. 2 and further considered in FIG. 3. Since the system of FIG. 4includes many units similar to units in the systems of FIGS. l, 2, and3, such units are identified by the same reference numerals. Units inthe system of FIG. 4 which are analogous to units of FIG. 1 areidentified by reference numerals of such analogous units with a factorof 400 added thereto. Units and elements first described 24 in thesystem of FIG. 4 are identified with numerals in the group 151-170.

In the system of FIG. 4, the output circuit of the amplifier 243 iscoupled through a parallel-tuned circuit 151 and an inductor 152, inseries, to a source of potential +B. Another parallel-tuned circuit 153is inductively coupled to the circuit 151 so as to effect a quadraturephase shift of the signal translated through the circuits 151 and 153,this coupling being discussed more fully hereinafter. The circuit 153has one terminal thereof coupled through a signal-sampling device 154,which ncludes a pair of oppositely poled diode circuits, to a winding ofa transformer 155. The other winding of the transformer 155 is coupledto an output circuit of the amplifier 35 and the other terminal of thetuned circuit 153 is connected through a winding 156 to ground. Aparallel-tuned circuit 157 is inductively coupled to the inductor 152 sothat effectively no phase shift of the signals translated through theinductor 152 and the tuned circuit 157 occurs. One terminal of the tunedcircuit 157 is coupled through a sampling device 158 similar to thedevice 154 to the winding of the transformer 155 while the otherterminal of the circuit 157 is connected through an inductor 159, aparallel-tuned circuit 160, and a load circuit161 in cascade, in theorder named, to ground. The tuned circuit 160 is resonant at the secondharmonic frequency of the NTSC subcarrier wave signal, that is, atapproximately 7.2 megacycles and the load circuit 161 includes, inparallel, a seriesresonant circuit for shunting high-frequency signalsand a high-impedance circuit for low-frequency signals to develop alow-frequency M-Y correction signal. A parallel-resonant circuit 162tuned to the fundamental frequency of the NTSC wave signal isinductively coupled to the winding 156 and another parallel-tunedcircuit 163 resonant at the third harmonic of the NTSC wave signal isinductively coupled to the winding 159. The circuits 162, 163, 16%, and161 are coupled in series, in the order named, and comprise an inputload circuit for an amplifier 164. The output circuit of the amplifier164 is connected to the cathode of the picture tube 30. The relativeimpedances of the units 162, 163, 160, and 161 are proportioned in amanner to be explained more fully hereinafter for reasons expressed atsuch time.

The circuit coupling the secondary winding of the transformer 34 to thegrid structure 33 in the picture tube 30 includes a condenser 165, achoke 166, and a tapped portion of a voltage divider 167 in seriesbetween one terminal of the secondary winding of the transformer 34 andthe center tap of such winding. The voltage divider 167 is connectedbetween two high-potential sources so that there is substantially a 500volt drop thereacross.

Explanation of operation of image-reproducing system of FIG. 4

For reasons relating to minimizing of color cross talk, it is sometimesbeneficial to utilize modulation components of the modulated NTSCsubcarrier wave signal other than the color-difference components B-Y,R-Y or the color components G, R and B. Two components I and Q have beenutilized and they have phase relations and magnitudes with respect tothe B--Y and R-Y components previously considered herein such asrepresented by the vector diagram of FIG. 4a. These I and Q modulationaxes of the modulated NTSC subcarrier wave signal are utilized in theoperation of the system of FIG. 4.

In the system of FIG. 4 a unidirectional bias potential is developed atthe tap point of the voltage divider 167 and applied as a bias betweenthe pairs of grids individually positioned behind the red and bluephosphors. This bias causes the beam, which would normally have eachvertical excursion thereof centered on each green phosphor as a line isbeing scanned, to be displaced from such center position so that thecolor-switching signalI tends to cause the beam to impinge on either thered or plue phosphors .for a longer time. As explained previouslyherein, the red phosphor is relatively ineiiicient with respect to thegreen land 'blue phosphors and thus in the system of FIG. 4 the biaspotential is such as to cause the center of the vertical excursions ofthe beam to be displaced on each green phosphor toward the adjacent redphosphor. This causes the beam to impinge for a longer time on the redphosphor, suiiiciently long to compensate for its relative ineiiiciency,and for a shorter time on the blue phosphor. Also the times during whichthe beam impinges on the green phosphor are no longer 180 apart on thecolor-switching cycle. Thus the type of modified signal discussed withreference to the prior figures hereinshould not be used with the systemof FIG. 4 if a high degree of color fidelity in reproduction is desired.However, by utilizing the analytical approach discussed hereinwithrespect to FIG. 1b, the proper signal for application to a picture tubeemploying color-balance compensation by decentering the electron beamwith respect to the vertical mid-point of the green phosphors may bedeveloped.

In developing Equations 1 and 2 `vvith respect to FIG. lb and the otherequations following therefrom, it was explained that a samplingoperation could be defined in terms of a Fournier series# and that thecomposite effect of many sampling operations in a color-'switching cyclecouldr be developed by combining the effects of the samples. In `thesystem of FIG. lb such samples were symmetrical in quantity and withrespectto the three primary colors. In the beam decentered system ofFIG. 4 suc-hsarnples are not Vsymmetrical with respect to the threecolors; Taking suchyasymmetry into consideration, and 'using the type ofanalysis employed with respect to FIG. 1b, equations can be developedwhich define the type of modified NTSC signal to be employed lin thesystem of FIG. 4. Such .analysis leads to thefmding that the M-Ycorrection signal should be approximately .4Q and that themodiiied NTSCsubcarrier wave signal should include 'la Ifundamental component ofapproximately +1.11, a secondv harmonic component of approximately.'-{.7 7Q, and a third harmonic comlponent of approximately -1. 2Q Whereall such intensi-ties ,are 'with respect to an intensity of unity forthe brightness signal Y; The system 413 of' FIG. 4 effects` suchcombination of signal components to develop a modified NTSC subcarrierwave signal suitable for utilization in the picture tube 30.

Considering now the operation of the system 413 of FIG. 4, as previouslydescribed herein, the 3.6 megacycle signal developed in the outputcircuit of the ampliiier 35 and employed as the color-switching signalis in phase with .the I axis of the modi-hed NTSC modulated subcarrierwave signal as applied to the cathode of the picture tube. This 3.6megacycle signal is applied through the transformer 155 to each of thesampling devices 154 and 158. The NTSC subcarrier wave signal applied tothe tuned circuit 151 is inductively coupled to the tuned circuit 153and applied to the sampling device 154. The phasing of the NTSC signaltranslated through the circuits -151 and 153 is modified so that the Iaxis of such signal is in phase with the 3.6 megacycileireference signalapplied to the device 1'54 and thus components along the I axis aretranslated through the device r154 and inductivley coupled throu-gh theWinding 156 for developing a 3.6 megacycle signal including such Icomponents in the tuned circuit 162 with an intensity olf |1.1I. TheNTSC signal applied to the winding 15.2, inductively coupled through theAtuned circuit 157 and applied to the sampling device 158, has the Qaxis thereof in phase with the 3.6 megacycle reference signal alsoapplied to the sampling device 158. Therefore, the modulation componentsalong such axis are translated through the device 158, through thewinding 159 and applied to the circuits 163', 160, and 161. In thecircuit A1621 a third harmonic 0r 10.8 megacycle sign-al isdevelopedwhich is effectively modulated solely by -a -l2Q component; Inthe `circuit 160 a second harmonic r 7.2 megacycle signal is developedwhich is effectively modulated by +.77Q and in the circuity 161 alow-frequency'LllQ signal is developed., The latter .4Q componentrepresents the previously considered M -Y correction signal 4while thesignals in ythe circuits 162, 163, and 160 combine to develop acompositesignal which is proper forntilization withthe picture tube 30wherein the beam has .been decentered so as to impinge for a longer timeon the` red phosphors. This modified subcarrier =Wave signaland thelow-frequency signal which is the equivalent of the M-Y correctionsignal are amplified in the unit 164 kand applied to :the cathode of thepicture tube- 30. The-luminance signal `is applied to the control`electrode of suchtube. The tube 30 operates in the manner previouslydescribed herein to reproduce a color imagefrom such applied signals.

' It should be noted .with respect to the system of FIG. 4 that, Whereasin the systems of FIGS. 1, 2, and .3 there was no detection of greenlfrom the fundamenta-l signal thus resulting in lack of constantluminance requiring the development of an M-I correction signal utilizedto correct for both the fundamental and-second harmonic signals, thereis some detection of green from the fundamental signal in the system ofFIG. 4 because of the exciting of the green phosphors at other thanphase points on the :color-switching signal. The amount offdetection ofthe .green component Afrom the lfundamental signal in FIG. 4 can be so,adjusted by a selected amount of decentering of the beam as to effectsuficient green to combine with the red andblue detected from thefundamental signal togive constant-luminance operation for thefundamental signal. In such case the luminance correction signaldeveloped inthe circuit l161 of FIG. 4 need only correct Afor luminanceerrors in the higher frequency-modulated subcarrier wave signals appliedto the picture tube.

From the foregoing description, it will be yapparent that a chrominancecomponent-selection system constructed in accordance with 'the inventionhas the advantage that it is capable of selecting a component of achrominance subcarrier along ya given axis without requiring decodingand Ire-encoding of the subcarrier signal.

While there have been described .what are at present considered to bethe preferred embodiments of this invention, it will be obvious to thoseskilled in the art that various changes Kand modifications may be madetherein without Ideparting from the invention, yand it is, therefore,aimed to cover all such changes and modifications as fall -within thetrue spirit and'scope of the invention.

What is claimed is:

l. In a color-television receiver, a system vfor selecting a chrominancesubcarrier rcomponent along a predetermined axis of a receivedchrominance subcarrier signal comprising: first circuit means forsupplying a chrominance subcarrier signal; second circuit means forsupplying la reference signal having a second harmonic frequencyrelation to said subcarrier signal; and third circuit means coupled tosaid first. and second circuit means and being, under the control ofsaid reference signal, responsive to said subcarrier signal during phaseangles when a selected subcarrier signal component valong apredetermined axis has maximum magnitude for developing a subcarriersignal representative of said selected subcarrier component to thesubstantial exclusion of its quadrature component.

2. In a color-television receiver, a system for selecting a chrominance-subcarrier component along a predetermined axis of a receivedchrominance subcarrier signal comprising: first circuit means -forsupplying a chrominanee subcarrier signal; second circuit meansforsupplying a reference signalhaving. arsecond harmonic frequencyrelation to said subcarrier signal; and third circuit means coupled tosaid first and second circuit means and being, under the control of saidreference signal, responsive to said subcarrier signal during phaseangles when a selected subcarrier signal component along a predeterminedaxis has Amaximum magnitude for developing a subcarrier signalrepresentative of said selected subcarrier component to the substantialexclusion of its quadrature component and having the same frequency assaid supplied subcarrier signal.

3. In a color-television receiver, a system for selecting a chrominancesubcarrier component along a predetermined axis of a receivedchrominance subcarrier signal comprising: first circuit means forsupplying a chrominance subcarrier signal; second circuit means forsupplying a reference signal having a second harmonic frequency relationto said subcarrier signal; and third circuit means coupled to said firstand second circuit means and effective to translate said subcarriersignal during phase angles when a selected subcarrier signal componentalong a predetermined axis has maximum magnitude and including meansresponsive to said reference signal for periodically shunting said firstcircuit means during intervening phase angles for developing asubcarrier signal representative of said selected subcarrier componentto lthe substantial exclusion of its quadrature component.

. In a color-television receiver, a system for selecting a chrominancesubcarrier component along a predetermined axis of a receivedchrominance subcarrier signal comprising: first circuit means forsupplying a chrominance subcarrier signal; second circuit means forsupplying a reference signal having a second harmonic frequency relationto said subcarrier signal; and third circuit means coupled to said firstand second circuit means and effective to translate said subcarriersignal during phase angles when a selected subcarrier signal componentalong a predetermined axis has maximum magnitude and including anonconductive diode circuit periodically conditioned for conduction bysaid reference signal for periodically shunting said first circuit meansduring intervening phase angles for developing a subcarrier signalrepresentative of said selected subcarrier component to the substantialexclusion of its quadrature component.

5. In a color-television receiver, a system -for selecting a chrominancesubcarrier component along a predetermined axis of a receivedchrominance subcarrier signal comprising: first circuit means forsupplying a chrominance subcarrier signal; second circuit means forsupplying a reference signal having a second harmonic frequency relationto said subcarrier signal; and third circuit means coupled to said firstand second circuit means and including means responsive to saidreference signal for periodically shunting said first circuit meansduring given phase angles when a selected subcarrier signal componentalong a predetermined axis has a maximum magnitude substantially toprevent translation of said subcarrier component along a first pathwhile allowing translation of its quadrature component along said firstpath and effective to translate said subcarrier signal along a secondpath during said given phase angles and effective to prevent translationof said subcarrier signal along said second path during interveningphase angles for developing along said second path a subcarrier signalrepresentative of said selected component to the substantial exclusionof said quadrature component.

6. ln a color-television receiver, a system for selecting a chrominancesubcarrier component along a predetermined axis of a receivedchrominance subcarrier signal comprising: first circuit means forsupplying a chrominance subcarrier signal; second circuit means forsupplying a reference signal having a second harmonic frequency relationto said subcarrier signal; and third circuit means coupled to said firstand second circuit means and including a normally nonconductive triodecircuit periodically conditioned for conduction by said reference signalfor periodically shunting said first circuit means during given phaseangles when a selected subcarrier signal component along a predeterminedaxis has a maximum magnitude substantially to prevent translation ofsaid subcarrier component along a first path while allowing translationof its quadrature component along said first path and periodicallyeffective to translate said subcarrier signal along a second path duringsaid given phase angles and effective to prevent translation of saidsubcarrier signal along said second path during intervening phase anglesfor developing along said second path a subcarrier signal representativeof said selected component to the substantial exclusion of saidquadrature component.

7. In a color-television receiver, a system for selecting a chrominancesubcarrier component along a predetermined axis of a receivedchrominance subcarrier signal comprising: first circuit means forsupplying a chrominance subcarrier signal; second circuit means forsupplying a reference signal having a second harmonic frequency relationto said subcarrier signal; and third circuit means coupled to said firstand second circuit means and including a nonconductive circuitperiodically conditioned for conduction by said reference signal forperiodically translating said subcarrier signal during given phaseangles when a selected subcarrier signal component along a predeterminedaxis has maximum magnitude for developing a subcarrier signalrepresentative of said selected subcarrier component to the substantialexclusion of its quadrature component.

8. In a color-television receiver, a system for selecting a chrominancesubcarrier component along a predetermined axis of a receivedchrominance subcarrier signal comprising: first circuit means forsupplying a chrominance subcarrier signal; second circuit means forsupplying a reference signal having a second harmonic frequency relationto said subcarrier signal; and third circuit means coupled to said firstand second circuit means for effectively deriving subcarrier signalcomponents of original phase sequence and subcarrier signal componentsof reversed phase sequence including a given quadrature component ofsubstantially the same magnitude as and of opposite polarity to thecorresponding quadrature component of said derived subcarrier signalcomponents of original phase sequence for developing a resultantsubcarrier signal representative of a selected chrominance component tothe substantial exclusion of said corresponding quadrature component.

9. In a color-television receiver, a system for selecting a chrominancesubcarrier component along a predetermined axis of a receivedchrominance subcarrier signal comprising: first circuit means forsupplying a chrominance subcarrier signal; second circuit means forsupplying a reference signal having a second harmonic frequency relationto said subcarrier signal; and third circuit means coupled to said firstand second circuit means and including means responsive to saidreference signal for periodically shunting said first circuit meansduring given phase angles for effectively deriving subcarrier signalcomponents of original phase sequence and subcar- Iier signal componentsof reversed phase sequence including a given quadrature component ofsubstantially the same magnitude as and of opposite polarity to thecorresponding quadrature component of said derived subcarrier signalcomponents of original phase sequence for developing a resultantsubcarrier signal representative of a selected chrominance component tothe substantial exclusion of said corresponding quadrature component.

l0. An image reproducing system for a color-television receivercomprising: first circuit means for supplying a brightnessrepresentative signal and a subcarrier signal modulated by a pair ofsignal components in quadrature phase relation; second circuit means forsupplying a reference signal having a predetermined frequency relationto the subcarrier signal; signal derivation means coupled to said firstand second circuit means, having two output circuits, and being, underthe control of the reference signal, responsive to the subcarrier signal

